Process for producing methacrylate/nu-methylolacrylamide polymers



Unite States Patent "ice Bfll'iflldd Patented den 2?, l tid 3,117,108PROCEES FGR PRUDUCLQG METHAQRYLATE/N- R'ZETHYLGLAQRYLANHDE PQLYMIERSLouis Gerald Calvete, Welwyn Garden Qity, England,

assignor to imperial Chemical industries Limited, London, England, acorporat n of Great Britain No Drawing. Filed Nov. 10, 195'), Ser. No.351,959 Claims priority, application Great Britain Nov. 28, 19 58 4Qlaims. (61. 260-805) This invention relates to improvements in polymersof methyl me-thacrylate.

in the past a number of methods have been proposed for the production ofmethyl methacrylate polymers having improved resistance to organicliquids and a reduced tendency to distort or lose their shape whenheated. In a number of these methods it has been proposed tocopolyrnerise methyl methacrylate with a compound containing twopolymerisable double bonds e.g. ethylene glycol dimethacrylate. The useof such compounds leads, however, to certain disadvantage In particularthe copolymers obtained are considerably less thermoplastic thanpolymethyl methacrylate and it has been difficult, if not impossible, toshape them at elevated temperatures. A further disadvantage arises fromthe fact that during the copolymerisation of methyl methacrylate withsuch compounds the rate at which the mixture hardens is not uniformthroughout its volume. Consequently, the contraction of the mixturewhich takes place during polymerisation does not proceed uniformly andthe solid polymer obtained does not reproduce faithfully theconfiguration of surfaces, e.g. the Walls of a mould, by which it is confined during polymerisation.

it is an object of the present invention to provide compositionscontaining methyl methacrylate which on polymerisation yield solidpolymers that can be shaped at elevated temperatures and that can beconverted by a heattreatment into products that are more resistant toorganic liquids than the known homopolymers of methyl met 1- acrylate. Afurther obiect is to provide such compositions having the additionalcharacteristic that solid polymers prepared from them can be convertedby heat-treatment into products that have a reduced tendency to distortor lose their shape under the influence of heat.

According to the present invention, We provide a composition whichcontains methyl methacrylute with or without a lesser amount by weightof an ester of acrylic acid with a saturated rnonohyclric alcoholcontaining not more eight carbon atoms per molecule, and to each molarproportion of said methyl methacrylate and of said ester of acrylic acidif present, from 0.005 to 0.50 molar proportions of a substitutionproduct of acrylamide or methaerylamide in which one of the hydrogenatoms attached to the nitrogen atom has been substituted by a methylolgroup or by an allzoxy substituted methyl group in which the alltoxygroup contains not more than 8 carbon atoms, and from 0 to 0.25 molarproportions of acrylamide, methacrylaznide or a mono-N-substitutedacrylamide or methacrylamide in which the substituting group is not amethylol group or alkoxy substituted methyl group, the con-- positionbeing substantially free of any compound containing two or morepolymerisable double bonds. We prefer that the composition shouldcontain not more than 0.001 molar proportions of any compound containingtwo or more polymeris-able double bonds to each molar proportion ofmethyl methacrylate and of said ester of acrylic acid if present.

Also according to our invention we provide a process for producing sucha composition in whic methyl methacryl -te, with or without a lesseramount by weight of said ester of acrylic acid, is mixed together withacrylarnide or r ethacryl-arnide and formaldehyde in concentrationssuilicient to form said methylol substituted compound in saidproportions of from 0.005 to 0.50 molar proportions of said methylolsubstituted compound to each molar proportion of methyl methacrylate andof said ester of acrylic acid if present, and the mixture is heated.

The polymers obtained by polymerising compositions according to thisinvention are thermoplastic and can readily be shaped at elevatedtemperatures. On subjecting these polymers to a heat treatment theirresistance to organic solvents increases and their tendency to distortor lose their shape at elevated temperatures simultaneously decreases.The extent of the improvement in these respects increases as theproportion of the methylol or alkoxy methyl substituted amide present isincreased. The polymers obtained from compositions in which theproportion of the methylol or alkoxy methyl substituted amide is highe.g. in excess of (M0 molar proportions, in relation to the proportionof methyl methacrylate are substantially thermosetting and cannot bemoulded after heat treatment. Such polymers should therefore besubjected to any desired shaping operation before they are heattreated.Polymers prepared from mixtures containing relatively low proportions ofthe methylol or alkoxy methyl substituted amide on the other hand, e.g.not more than 0.05 molar proportions can still be shaped at elevatedtemperatures after heat-treatment.

Mono-N-methylol rnethscrylamide is the preferred methylol substitutedamide for use in compositions according to this invention as thepolymers then obtained show particularly high resistance to organicliquids and high heat distortion and demoulding temperatures afterheat-treatment. Particularly good results are achieved whenniono-N-methylol methaorylamide is used in conjunction withmethacrylamide.

Examples of mono-N-substituted amides that may be used in coniunctionwith the methylol or allroxy methyl substituted amide in compositionsaccording to this invention include N-rnethyl acrylamide and N-methylmethacrylamide.

The esters of acrylic acid that may be included are for example ethylacrylate, butyl acrylate and ethyl hexyl acrylate. The reason forincluding these copolymerising monomers is to make the copolymer moreeasily deformed when heat softened in the shaping operation. The amountsnormally required are from 0% to 15% by weight of the m ture of methylmethacrylate and the ester of acrylic The compositions of this inventionpreferably contain no compound containing two or more polymerisabledouble bonds in order to avoid the undesirable effects of such compoundsdescribed hereinbefore.

The compositions of this invention may be produced by mixing pro-formedingredients or alternatively in the case of the methylol substitutedamide, the compound may be prepared in situ by heating the correspondingamide with sulficient formaldehyde to form the methylol derivative inthe presence of all or a part of the methyl methacrylate and thereafteradding any required additional methyl methacrylate. if the methylolsubstituted amide is made in situ, the amide or the formaldehyde or bothmay if desired be added to the methyl methacrylate in portions orcontinuously. The formaldehyde may conveniently be used in the form ofan aqueous solution, cg. as formalin, and the reactants may be heatedtogether under reflux at atmospheric pressure. Suitable periods ofheating are of the order of 1 to 30 minutes. The Water present may thenbe separated by distillation; if the concentration of water present isnot large it may not be necessary to remove it and the mixture can beheated until a syrup is formed and polymerisation effected ashereinafter described. it the proportion of water present is lugs,separation may occur and for this reason its removal may be necessary.The presence of water may have a slightly adverse effect on the crazeresistance and softening point of the final polymer, and for this reasonit is in general preferred to remove the water before polymerisation.Instead of using formalin, gaseous formaldehyde may be passed into astirred and heated mixture of the methyl methacrylate and the amide.Gaseous formaldehyde for this purpose may be obtained for example, bypyrolysing paraformaldehyde, a-polyoxymethylene or a hemiformal, forexample, cyclohexyl hemiformal. In order to obtain a final polymer withthe most useful properties e.g. resistance to crazing, we prefer that toeach molar proportion of acrylamide or methacrylamide, there should beless than one molar proportion of formaldehyde. In particular, we preferthat to each molar proportion of acrylarnide or methacrylamide thereshould be from 0.25 to 0.75 of one molar proportion of formaldehyde.

The compositions of this invention may be polymerised by any desiredmethod. Since they contract in volume as they polymerise, it isnecessary when polymerisin g them in mould, to use a mould of the typein which the walls f the mould are capable of moving in such a way as tomaintain contact with the composition as it contracts. A convenient formof mould for the production of flat sheets consists of two parallelsheets of glass separated at their peripheries by a resilient gasket.Before compositions according to the present invention are introducedinto a mould of this type, they are preferably heated to about 100 C. inthe absence of a polymerisation catalyst, or in the presence of a verysmall concentration of catalyst e.g. approximately 0.001 to 0.005% ofbenzoyl peroxide based on the weight of the polymerisable constituentsof the composition, until their consistency thickens to that of a syrup.This facilitates the introduction of the composition into the mould andalso reduces the danger of the composition seeping between the gasketand the glass Walls of the mould. When converting the composition to asyrup We prefer to maintain the composition in alkaline conditionpreferably at pH 8 to 9 because under these conditions the syrup is keptin a condition in which it can be easily handled. The pH can becontrolled by the addition of alkali.

The conversion of compositions according to this invention to solidpolymers is preferably effected by beating them in the presence of afree radical yielding polymerisation catalyst. Any catalyst suitable forpolymerising methyl methacrylate may be used for this purpose. Suitablecatalysts thus include organic peroxides, e.g. benzoyl peroxide, laurylperoxide and the azo catalysts in which the valencies of the azo groupare attached to different non aromatic, preferably tertiary, carbonatoms, e.g. a, xazo-bis-isobutyronihile.

The heat-treatment to which the resulting polymer is subjected .in orderto develop its resistance to organic liquids and heat may be carried outeither before or after the polymer is removed from the mould. If thepolymer substantially thermosetting in character, however, and it isdesired to subject it to a shaping operation after removing it from themould, then the heat treatment must kcf course be deferred until afterthe shaping operation.

Temperatures between about 90 C. and the degrada- "tion temperature ofthe polymer are suitable for the heat- :treatment of the polymer. It ispreferred to use a temperature below about 185 C. in order to avoid therisk of degradation of the polymer. On the other hand, the period ofheating required decreases as the temperature increases and it istherefore preferred not to use temperatures below about 150 C. Withinthe temperature range of 150 C. to 185 C., periods of heating of theorder of 10 to 150 minutes are usually adequate.

The duration of the heat-treatment may be reduced by including in thecompositions of this invention a small proportion of an aliphatic acidthat is soluble in the composition e. g. methacrylic acid. This, ifused, is preferably added to the composition after it has been convertedinto a syrup and before its conversion into a solid polymer. Suitableproportions of methacrylic acid are of the order of 0.1 to 6% by weightof the methyl methacrylate originally present in the composition.Examples of other suitable acids are acrylic acid and maleic acid.

The heat-treated polymers produced from compositions according to thisinvention which are still capable of being shaped are particularlysuitable for such applications as aircraft canopies and windows, watchglasses and buttons which may come into contact with solvents e.g.during dry-cleaning. The substantially thermoset polymers areparticularly suitable for applications in which dimensional stability athigh temperatures is desired e.g. for the production of lightingfittings.

The polymers produced from the compositions of this invention are ingeneral also suitable for other applica tions of the type for whichpolymethyl methacrylate has hitherto been used. They are of courseparticularly suitable for use in applications involving contact withorganic liquids because of their high degree of resistance to attack andcrazing by such liquids.

Ancillary ingredients e.g. colouring materials, pigments, stabilisers orplasticisers e.g. dibutyl phthalate, may be added to the composition atany convenient stage.

Our invention is illustrated but not limited by the following examplesin which all parts are by weight.

Example 1 To 100 parts of methyl methacrylate were added 5.6 parts ofmethylacrylamide and 4 parts of formalin. The mixture was heated to C.at atmospheric pressure under reflux for 10 minutes. Water was thenseparated from the mixture by distillation, the water distilling in theform of an azeotropic mixture with methyl methacrylate. The temperatureof the mixture was raised to C. and maintained at this level until themixture thickened to a syrupy consistency. After cooling, benzoylperoxide and methacrylic acid were added to the mixture in proportionsof 0.1 part and 1 part, respectively, per 100 parts of the mixture. Themixture was poured into a fiat casting mould having movable glass wallsand polymerized to a solid sheet by subjecting it to a temperature of 56C. for a period of 8 hours and then to a temerature of 100 C. for afurther 3 hours. The sheet was then removed from the mould andheat-treated by suspending it in an oven at a temperature of 180 C. forZhours.

On immersing a piece of the resulting transparent sheet in chloroform at18 C. it did not swell beyond a weight increase of 250%. Under the sameconditions a sample of commercially available polymethyl methacrylatesheet dissolved completely.

Example 2 210 parts of methacrylamide and 37.8 parts of formalin with apH of 8.5, were added to 450 parts of methyl mcthacrylate monomer. Themixture was warmed until a clear homogeneous solution was obtained, andthe solution was then heated to 83 C. to remove the watermethylmethacrylate azeotrope. On removing the water, the solution hadthickened sufficiently to make it suitable for pouring into aglass-cell, although it was still freellowing. 0.7 parts of benzoylperoxide were added and sufficient methyl methacrylate monomer to makethe total weight 700 parts. The solution was placed in a cell made oftwo glasses separated by a distance of 0.160 by a resilient gasket roundthe periphery of the glass plates, and polymerised at a graduallyincreasing temperature from 50l00 C. On curing the sheet at C. acrosslinked sheet was obtained which increased less than 1% by weightwhen placed in chloroform for 36 hours. Commercial polymethylmethacrylate dissolved under these conditions.

Example 3 To 100 parts of methyl methacrylate were added 0.002 parts ofbenzoyl peroxide and parts of methacrylamide. The mixture was warmed todissolve the methacrylamide, after which 2.7 parts of formalin(containing 36% of formaldehyde on a weight basis) were added. Themixture was then filtered, and then heated to 80 C. until a syrup wasformed. The syrup was cooled and to it were added 0.1 parts of benzoylperoxide.

The syrup was placed in a glass cell as described in Example 2 andpolymerised at a gradually increasing temperature from 50 to 100 C. Thepolymerised sheet was removed from the cell and then maintained at 160C; for 20 minutes. The final polymer was insoluble in organic solvents.

I claim:

1. A process for the production of solid polymeric material by bulkpolymerization of a polymerizable composition comprising heating saidcomposition in the presence of a catalytic amount of a free radicalyielding polymerization catalyst until a solid polymeric sheet isformed,

said polymerizable composition consisting essentially of (a) amonoethylenically unsaturated monomeric ester material selected from theclass consisting of methyl methacrylate and mixtures of methylmethacrylate with up to of an ester of acrylic acid with a saturatedmonohydric alcohol containing not more than eight carbon atoms permolecule, and (b) from .005 to 0.50 molar proportions of said monomericester material of a substituted amide having the formula CHFCR.CO.NH.CH.OR

where R is selected from the group consisting of H and CH and R isselected from the group consisting of H and alkyl radicals containingnot more than 8 carbon atoms, and thereafter heating said polymericmaterial to a temperature within the range 150 C. to 185 C. to increaseresistance to solvents and deformation under the influence of heat.

2. A process according to claim 1 in which said substituted amide ismono-N-methylol methacryalmide and in which the proportion of saidsubstituted amide is from 6 0.10 to 0.50 molar proportions to each molarproportion of said monomeric ester material.

3. A process according to claim 1 in which said substituted amide ismono-N-methylolmethacrylamide and in which the amount of saidsubstituted amide is from 0.005 to 0.05 molar proportions to each molarproportion of said monomeric material.

4. A process for the production of a solid polymeric material by bulkpolymerization of a polymerizable composition comprising heating saidcomposition in the presence of a catalytic amount of a free radicalpolymerization catalyst until a solid polymer is formed,

said polymerizable composition consisting essentially of (a) amonoethylenically unsaturated ester material selected from the classconsisting of methyl methacrylate and mixtures of methyl methacrylatewith up to 15 of an ester of acrylic acid with a saturated monohydricalcohol containing up to eight carbon atoms per molecule, and (b) from0.005 to 0.50 molar proportions of said monomeric ester material of asubstituted amide having the formula CH CRCQNI-LCH OH in which R isselected from the group consisting of H and CH said substituted aminebeing the product obtained by heating a compound selected from the groupconsisting of acrylamide and methacrylamide with an aqueous solution offormaldehyde in suflicient quantity to form the methylol derivative,said heating being initially carried out under reflux and the waterpresent thereafter being removed by distillation, and thereafter heatingsaid polymeric material to a temperature within the range C. to C. toincrease resistance to solvents and deformation under the influence ofheat.

References Cited in the file of this patent UNITED STATES PATENTS2,761,856 Suen et a1. Sept. 4, 1956 2,794,016 Glenn et a1 May 28, 19572,940,943 Christenson et a1. June 14, 1960' 3,018,265 Tessmar Jan. 23,1962

1. A PROCESS FOR THE PRODUCTION OF SOLID POLYMERIC MATERIAL BY BULKPOLYMERIZATION OF A POLYMERIZABLE COMPOSITION COMPRISING HEATING SAIDCOMPOSITION IN THE PRESENCE OF A CATALYTIC AMOUNT OF A FREE RADICALYIELDING POLYMERIZATION CATALYST UNTIL A SOLID POLYMERIC SHEET ISFORMED, SAID POLYMERIZABLE COMPOSITION CONSISTING ESSENTIALLY OF (A) AMONOETHYLENICALLY UNSATURATED MONOMERIC ESTER MATERIAL SELECTED FROM THECLASS CONSISTING OF METHYL METHACRYLATE AND MIXTURES OF METHYLMETHACRYLATE WITH UP TO 15% OF AN ESTER OF ACRYLIC ACID WITH A SATURATEDMONOHYDRIC ALCOHOL CONTAINING NOT MORE THAN EIGHT CARBON ATOMS PERMOLECULE, AND (B) FROM .005 TO 0.50 MOLAR PROPORTIONS OF SAID MONOMERICESTER MATERIAL OF A SUBSTITUTED AMIDE HAVING THE FORMULA